Compound optical coupler and support mechanism

ABSTRACT

A support mechanism for protecting an object is described. The support system includes at least one support or friction ring for providing dynamic protection to the object. One embodiment includes a support ring having corrugated bumps. Another embodiment includes multiple support rings axially separated by spacers. In another embodiment a support mechanism is provided having at least one friction ring in combination with O-rings. A compound optical coupler is also described, which has a self-wetting clear optical coupling gel and an elastomeric load ring.

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 10/911,485, filed on Aug. 5, 2004, the entiredisclosure of which is incorporated herein be reference.

BACKGROUND

The invention generally relates to a protective mechanism and an opticalcoupler for use in systems for detecting the presence of hydrocarbonsduring mining or drilling operations. In the prior art, special opticalcouplers using Sylgard along with optical coupling oil have beenemployed with prior support systems to couple light from a scintillationelement into a light detector device. Such an optical coupler isdisclosed in U.S. Pat. No. 6,465,788, which is incorporated herein byreference in its entirety. One drawback to this approach is that, undersome extreme cases of high loads, uneven loads, or high vibration, oilused in the optical coupling may migrate out over time and result indegraded detector performance. Another drawback is that precisionfabrication and/or assembly tolerances must be maintained to preventloss of oil and degraded performance. Yet another drawback is thatparticulate contamination of the optical coupler can also cause loss ofoil and degraded performance. Another example of an optical interface isdisclosed in U.S. Pat. No. 6,222,192 to Sekela et al., the entiredisclosure of which is incorporated herein be reference.

Optical couplers made from self-wetting type materials (e.g., Wacker)have also been used. A drawback to these concepts is that theself-wetting materials exhibit viscous behavior and tend to flow outwardfrom the optical interface, allowing the optical interface retainingforce to be lost, and thus resulting in degraded performance. Wacker isan example of a self-wetting, optically clear material that is used foroptical coupling, and is sometimes the material of choice. The onlymaterials otherwise suitable for use inside a hermetic housing thatcontains a sodium iodide crystal, which also is capable of withstandingsubstantial dynamic loading and stresses, are not optically clear, andor do not provide a consistent high quality optical interface. However,Wacker and other similar materials, cannot withstand substantial loadingand/or will produce false scintillations under vibration due tomovements. Previous efforts to use this material include attempting tolimit longitudinal loading on the material but result in the crystalassembly moving longitudinally during high longitudinal vibration and/orresult in failure to move to maintain optical coupling under largechanges in temperature.

Nuclear detectors, such as gamma detectors, have been used in miningapplications and oil drilling operations for many years. In particular,gamma detectors have been used to measure the radiation that emanatesfrom the formations surrounding the mining or drilling equipment. Suchgamma detectors operate by utilizing the differences between the naturalradioactivity of the target formation and the natural radioactivity ofthe adjacent formations to determine the boundaries between theseformations. In the case of mining potash, the most desirable material tobe mined from the formation is the most radioactive, typically beingsurrounded by salt or lower grade mineral.

Gamma detectors are sensitive and must be protected from harshenvironments to survive and to produce accurate, noise free signals.This protection must include protection from physical shock and stress,including force, vibration, and abrasion, encountered during solidmineral mining and oil drilling operations. However, the closer inproximity the gamma detector is to the mineral being mined or drilled,the greater is the shock, vibration and stress to which the detector issubjected.

The presence of armor, which is required to protect the detector,further limits the available space. An explosion-proof housing takes upeven more of the available space, and often results in reducing thediameter of the photomultiplier tube. When light detecting devices ofrelatively low mass density are used in connection with scintillationelements having a relatively high mass density, a special means ofsupport is needed to reduce rotation moments when under high vibrationor high shock. Lower cost for providing protection for the detector isalso needed.

Advances have been made in recent years that improve the survivabilityand performance of gamma detectors that are used in mining, drilling,and other harsh environments. Yet, there remains a need for furtherimprovements. One area of need arises whenever large scintillationcrystals are used in a harsh environment such as mining. Long term wearand damage to the support system from continual high shocks can occurdue to the larger mass of the scintillation element. Shock isolationmust be done with sufficient care to not damage the interface betweenthe crystal and the light collecting element. Another area of need isfor a support system that can be designed with less engineering andanalytical expertise, so that components can be fabricated with moreease and at a lesser cost.

A support system must be very effective in protecting the detector fromthe harsh vibrations and shock, but must also do so while consuming asmall amount of space. Similarly, in mining operations, the outerportions of the detector and the armor must provide a high level ofshielding from unwanted radiation and must protect the detector fromimpact and abrasion, all with a minimal use of space.

Radial springs, although effective in other applications, have not beenutilized in subject applications, because, for example, radial springshave been found to be difficult to install, particularly for largescintillation elements and especially for large detectors. Also, theselection of the width, thickness, and design of radial springs in theapplicable spaces of gamma detectors has been found to be complex, thusdiscouraging their use in some instances.

In the prior art, detectors have been protected by a plurality ofsprings which extended along the axial length of the detector or itsscintillation element. An example of such a support system is a flexibledynamic housing, as disclosed in U.S. Pat. Nos. 6,452,163 and 6,781,130,which are incorporated by reference herein in their entireties. Onedrawback of such systems is that the springs extend along the axiallength of the scintillation element and as such can block radiation fromreaching the scintillation element, which is particularly importantwhere rapid motion of the cutter necessitates obtaining the maximumpossible gamma count rate. Moreover, the springs of the flexible housinghave to be custom made for this specific industrial application. Alsothe annular gap that exists between the scintillation element and itsrigid housing is not always uniform, such as because of dimensions oftolerance. This may complicate the installation or sizing of the system.

Flexible dynamic housings and flexible sleeves helped to solve someproblems. One very important characteristic of these supports is thereliance upon friction to hold the scintillation element,photomultiplier tube, and other elements in position during highvibration, while allowing for thermal expansion and shock. This relianceupon friction, instead of elastomeric materials reduces resonances,providing a dynamic transmissibility of near unity through mostfrequencies of concern and then provides effective dynamic damping oncethe friction is overcome. However, complexities in their design andfabrication resulted in higher cost than desired, requiring specialengineering processes, and specialized fabrication procedures.Experience has shown that there is a need to improve upon the advantagesof using metallic supports and the use of friction to improve theability to withstand high vibration and high shock as when used onrotary cutters. Improvement is needed to reduce design and fabricationcomplexity, and thereby reduce cost.

Another support mechanism for a detector is disclosed in pendingapplication Ser. No. 10/270,148, which is incorporated herein byreference in its entirety. This type of support mechanism is a flexiblesupport sleeve which extends along the length of the detector orscintillation element, and suffers from the same drawbacks discussedabove with respect to the springs. Furthermore, very high shockconditions, particularly for larger crystals, can over stress flexiblesleeves at the bends of such sleeves, causing the contact pressure to bereduce and thereby having insufficient friction remaining for goodsupport.

There remains a need for an optical coupling system that is lesssensitive to fabrication/assembly tolerances, high/uneven loads, andhigh vibrations. There is also a need for a simplified, lower coststructure and method for supporting instrumentation packages andsensors, such as gamma detectors. A means for supporting sensitiveelements, which have substantially a cylindrical shape, is needed towork in cooperation with other suitably chosen support elements. A moresuitable method of supporting sensitive elements so as to produce lesscompression of optical reflecting material is also needed.

Through the years, even at the present time, use has been and is beingmade of elastomeric or rubber materials in an effort to protectscintillation elements, photomultipliers, electronics, and assemblies ofthese items while being used in harsh environments. Although elastomershave proven to useful for cushioning high shock, high vibration combinedwith high shock has proven to be very challenging for protecting fragileelements such as sodium iodide crystals or cesium iodide. If widetemperature excursions are also involved, the problem is even morechallenging. There are fundamental reasons why this is the case. For onething, these materials, which are much softer than metals, tend toproduce a low resonant frequency. This contributes to higher forcesbeing placed upon the objects being protected. Resonating at lowerfrequencies results in greater displacements of the elements andincreases the probability of spontaneous noise generation and/or damage.

In an effort to reduce these effects, one may compress the materialsaround the object being protected so that there is less room for it tomove. If subjected to large temperature changes as is experienced duringdrilling into the earth or on hot machinery during cutting, thescintillation element expands toward the metallic shield, thus placingexcessively high pressure on the element. This is made worse by theexpansion of the elastomeric or silicone rubber material, which usuallyhas a very large coefficient of expansion as compared to other parts ofthe support system. Not only can these high forces damage the elementsbeing supported but they can cause interfacing element such as ascintillation element to be pulled away from the photomultiplier. Tryingto overcome such a separation by placing more force onto the interfaceby using larger springs to force the two together has sometimes beenshown to break the face of the photomultiplier tube, or the coupling, orthe scintillation element. Yet, attempts to overcome this problem bymechanically limiting the forces placed on the interface tends torecreate the problem trying to be solved. Reduction of the restrainingforces allows the interfacing elements to resonate in their longitudinaldirection.

Added to the above is the fact that the internal damping characteristicsof elastomeric materials or silicone rubber are poor compared to that ofsliding friction. The result is that when resonance is made possible bythe geometric considerations described above, the magnitude of theresonance is greater than it would be if sliding friction were moreprevalent. Thus, the limits of applicability for such materials do notsatisfy the needs of the industry.

SUMMARY

The inventions provide a gamma detector which, in some aspects, may beutilized in solid mineral mining, such as coal, potash and trona, oilwell drilling and/or servicing operations, de-gassing of coalformations, and logging of solid mineral formations. In one aspect ofthe inventions, the gamma detector includes a scintillation element.

The fundamental limiting factors related to the use elastomers and otherrelatively soft materials, when both high vibration and high shock areencountered, have been substantially overcome with earlier inventionsthat employ metallic supports. This use of metallic supports has beensuccessful to a considerable degree through the reliance upon frictionto restrain elements being protected from high vibration and high shock,and even with changes in temperature. This current inventionsubstantially overcomes weaknesses remaining with the earlier metallicsupports by use of friction rings, and also incorporates the combinedimprovements of a compound coupler arrangement and friction rings.

The current invention provides for the use of metallic support ringsthat utilize friction to support instruments in near-rigid dynamic statethrough most of the vibration conditions, which helps to maintain a highresonant frequency. When the friction restraint forces are overcome byhigh shock, so that the object being supported, such as a scintillationelement or photomultiplier tube or other instrumentation element, beginsto move, the resulting sliding friction provides a high degree ofdamping. For extremely harsh conditions, O-Rings are added to serve asshock absorbers and to limit the movement of the elements beingsupported.

Friction rings used in combination with O-rings and a compound opticalcoupler, all within a hermetically sealed shield provides for anextremely robust configuration that also provides for improved operatingperformance.

Numerous mechanical details are provided in the artwork andspecifications for earlier patents, which in many cases may beapplicable to the current invention for certain specific applicationrequirements. Someone reasonably skilled in the art can be expected tomake appropriate use of those details, using the current invention.

In one aspect, the invention provides a scintillation element packagecomprising a scintillation element; a housing encompassing thescintillation element; and a support mechanism including at least onesupport ring, the support mechanism being between the scintillationelement and the housing.

In another aspect, the invention provides a gamma detector comprising: aphotomultiplier tube; a first housing surrounding the photomultipliertube; and a support mechanism including at least one support ringsupporting the photomultiplier tube.

In yet another aspect, the invention provides a support mechanismcomprising: a rigid housing and a support mechanism having a supportring, wherein the support mechanism at least partially surrounds anobject to be protected, and wherein the support mechanism is between therigid housing and the object.

In still another aspect, the invention provides a detector comprising: ascintillation element; a first housing and a second housing; an innersupport mechanism including at least one support ring, said innersupport mechanism supporting the scintillation element; an outer supportmechanism including at least one support ring, said outer supportmechanism supporting the scintillation element and surrounding saidinner support system.

In another aspect, the invention provides a compound optical couplingassembly comprising a self-wetting optical coupling gel in an interiorportion of the optical coupling assembly, and an elastomeric load ringradially outward of the self wetting optical coupling gel. In order topermit use of a soft optical coupling material, such as Wacker, which isoptically clear or having other superior properties, a relativelytransparent load bearing material, such as Sylgard, surrounding thenon-load bearing coupling material. Another way to make the opticalcoupling is to bond the crystal to the photomultiplier tube.

This invention provides a low cost method of supporting instrumentationsystems and/or subsystems within mining equipment, or other equipmentused in harsh environments. The invention provides a scintillationelement package that includes a scintillation element, a shieldencompassing the scintillation element, and a support mechanism having asupport ring at least partially surrounding the scintillation elementwithin the shield, the support mechanism providing support for thescintillation element.

The invention also provides, in one aspect, a support mechanism thatincludes a support ring surrounding and protecting an object to beprotected, wherein the support mechanism provides support for theobject. In another aspect, the invention provides a support mechanismhaving a support ring including an inner support mechanism surroundingand protecting an object to be protected and an outer support mechanismsurrounding the inner support mechanism, the outer support mechanismfitting within a cavity.

In another aspect, the invention provides a detector comprising ascintillation element, a housing encompassing the scintillation element,and a support mechanism including at least one friction ring, whereinthe support mechanism is between the scintillation element and thehousing. In yet another aspect, the invention provides a gamma detectorsupport mechanism, comprising a rigid housing and a support mechanismhaving at least one friction ring and at least one shock ring, whereinthe support mechanism is at least partially surrounding an object to beprotected, wherein the support mechanism is between the rigid housingand the object.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an armored housing for solid mineralmining use having a gamma detector support mechanism constructed inaccordance with an embodiment of the invention.

FIG. 2 is a cross-sectional view along the length of the gamma detectorof FIG. 1.

FIG. 3 is a cross-sectional view taken along line III-III of FIG. 2.

FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. 2.

FIG. 5 is a perspective view of a support ring of the support mechanismof FIG. 1.

FIG. 6 is a cross-sectional view of a gamma detector having a supportmechanism in accordance with an embodiment of the invention.

FIG. 7 is a cross-sectional view of a gamma detector having a supportmechanism in accordance with an embodiment of the invention.

FIG. 8 is a close-up view of FIGS. 6 and 7.

FIG. 9 is a cross-sectional view of an optical coupler constructed inaccordance with an embodiment of the invention.

FIG. 10 is a cross-sectional view along the length of a gamma detectorconstructed in accordance with another embodiment of the invention.

FIG. 11 is a close-up cross-sectional view of a portion of FIG. 10.

FIG. 12 is a close-up cross-sectional view of a portion of FIG. 10 inaccordance with another embodiment of the invention.

FIG. 13 is a top view of a corrugated sheet for a friction ring of thesupport mechanism of FIG. 10.

FIG. 14 is a side view of FIG. 10.

FIG. 15 is a view of an assembled friction ring of the support mechanismof FIG. 10.

FIG. 16 is an illustration of a liner in accordance with a preferredembodiment of the invention.

FIG. 17 cross-sectional view of the gamma detector having a supportmechanism in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates a gamma detector 20 installed into armor 70 formounting a mining module for use in solid mineral mining operations. Asshown in FIG. 1, the detector 20 is protected by armor 70 thatsurrounds, shields, and supports the detector. The detector 20 also maybe used in conjunction with oilfield operations, without the armor 70.FIG. 2 shows a cross-sectional view of the gamma detector 20. FIGS. 3and 4, which are cross-sectional views of FIG. 2, show the variouscomponents that protect the scintillation element 50, the electronics 57and other sensors. These multiple levels of protection are described indetail below.

With reference to FIGS. 1 and 2, gamma rays 28 entering the gammadetector 20 pass through a non-metallic window 71 to reach thescintillation element 50 within the detector 20. Other windows 65 (FIG.3) have been cut into a rigid dynamic enclosure 80 which surrounds thescintillation element 50.

Next, with reference to FIG. 2, the general function of the detector 20will be described. A scintillation element 50 responds to gamma rays 28that have been emitted from rocks in the soil. The response of element50 is to produce a tiny pulse of light that travels to a window 52 atthe window end of the scintillation element 50 or is reflected into thewindow 52 by a reflector 67 (FIG. 3) that is wrapped around thescintillation element 50. The light pulse travels through a firstoptical coupler 51, through the window 52, and through a second opticalcoupler 53 into the faceplate of a light detecting element, shown hereas a photo-multiplier tube 55. An electrical pulse is generated by thephoto-multiplier tube 55 and sent to electronics element 57.

The photo-multiplier tube 55, the electronics element 57 and anaccelerometer 60 are located in an assembly called a photo-metric module58. Since components within the photo-metric module 58 utilizeelectricity, it is necessary that it be enclosed in an explosion-proofhousing 59 to avoid accidental ignition of gas or dust that may be inthe vicinity of the detector 20. Also, the explosion-proof housing 59serves as an effective barrier that protects the electrical elements 57and the accelerometer 60 from the strong electromagnetic fieldsgenerated by heavy electrical equipment.

Better details of the protective elements are shown in FIGS. 3 and 4.The first view in FIG. 3 shows a support mechanism 100 that surroundsthe scintillation element 50, and protects it from high levels of lowerfrequency vibrations. The support mechanism 100 will be described ingreater detail below. The support mechanism 100 between thescintillation element 50 and the scintillation shield 63 supports thefragile scintillation element 50 and provides a high resonant frequencyso that it will not resonate with lower frequency vibrations that passthrough the outer housing. The outer housing 82 encloses another supportmechanism 100, the rigid enclosure 80 and a rigid elastomeric shockabsorbing sheath 81 which surrounds the enclosure 80.

A typical size scintillation element 50 for this application is 1.4inches in diameter by 10 inches in length, but may be as large as 2inches in diameter. The resonant frequency of these outer supportelements 81, 80 protect against shock and isolate the scintillationelement 50 from high frequencies.

FIG. 4 illustrates a view of a photo-metric module including aphoto-multiplier tube 55 inside a first housing 58, which is within theexplosion-proof housing 59. The support mechanism 100 is located atthree radial elevations about the photo-multiplier tube 55: between thephotomultiplier tube 55 and the first housing 58; between the firsthousing 58 and the explosion-proof housing 59; and between theexplosion-proof housing 59 and the rigid enclosure 80.

The elastomeric shock-absorbing sheath 81 fully covers the entire rigiddynamic enclosure 80. It should be noted that this sheath 81 servesother useful purposes. It provides good mechanical compliance with thearmor 70. This is particularly important during installation in whichdust and particles will be present. Another purpose of the sheath 81 isto prevent water or dust from entering through the window in theenclosure 80. The accelerometer module 60 is afforded the same criticalprotection from the harsh environment as the photo-multiplier tube 55.

In use, there is a need to firmly hold the light collecting element,which in this case is the photo-multiplier tube 55, so that it remainsfixed in position relative to the window 52 through which the light ispassing from the gamma detector scintillation element 50. This isespecially important in the disclosed embodiment because the exemplaryoptical coupling between the photo-multiplier tube 55 and the window 52is a two-piece compound coupling. One piece of the coupling is a soft,self-wetting pad typically made from a material called Wacker.Surrounding this inner coupling is a ring made from a more substantialmaterial such as Sylgard, also pliable, optically transparent material.The self-wetting optical coupler of the invention will be discussed ingreater detail below.

To work properly, the photo-multiplier tube 55 must not be free to movemore than a few thousands of an inch in the radial direction, while atthe same time, be pushed with a uniform force against the couplingelements and by a spring. To accomplish these dual requirements, thephoto-multiplier tube 55 must be sufficiently free to move in thelongitudinal direction while having its motion in the radial directionsignificantly restrained. Moreover, thermal expansion must not interferewith the two requirements discussed above.

These requirements are accomplished by the support mechanism 100 of thepresent invention. The support mechanism 100 comprises support ringswhich are placed around the photo-multiplier tube 55. The supportmechanism 100 will be described with reference to FIGS. 5 and 6. A maincomponent of the support structure 100 is a support ring 102, an exampleof which is shown in FIG. 5. Such a support ring 102 is commonlyreferred to as a tolerance ring in several industrial applications. Onemanufacturer of such rings is USA Tolerance Rings in Pennington, N.J.

The tolerance, or support ring is a device that facilitates fitting ofconcentric cylindrical parts. The support ring 102 has corrugated bumps104 which have a height 112. The support ring 102 also has a height 110and a diameter 114, and may have a rim 108. In the example shown, thecorrugated bumps extend, or face, toward the center of the support ring102. The inward facing corrugated bumps 104 compress in proportion totorque or radial load for wider dimensional tolerance. The support ring102 is not continuous, and has an opening 103. In use, the opening 103allows the support ring 102 to flex to accommodate different diameters,to move and to absorb shock and to thermally expand. In a preferredembodiment, a support ring with a part number of ANL-R8-9-S from USATolerance Rings can be used. Such a support ring has a diameter 114 ofapproximately 1.125 inches, a height 110 of approximately 0.313 inches,and a bump height 112 of approximately 0.25 inches. However, the heights110, 112 of the support ring 102 and bumps 104, and other parameters,may be varied to accommodate design parameters.

The support ring 102 is a frictional fastener, capable of handlingdirect torque transfer, torque slip, axial retention, controlledcollapse and radial loading between mating cylindrical components. It isa corrugated metal strip that acts as an interface between twomechanical objects, to secure one to the other by interference fit. Thecorrugated bumps 104 deflect and allow the support ring 102 to act likean elastic shim.

The number of the support rings 102 is chosen depending on theconfiguration of the photo-multiplier tube 55. In an exemplaryembodiment, between two and five support rings are used. With referenceto FIG. 6, three support rings 102 are shown supporting thephoto-multiplier tube 55. The support rings 102 may be held in place bymetal tape or a metal retainer, designated by numeral 106. The metaltape 106 has an adhesive material on its inward facing surface. Themetal tape, or retainer 106, is installed about the housing 120 of thephoto-multiplier tube 55. The metal tape or retainer 106 also functionsas a spacer to laterally separate the support rings 102. The supportrings 102 do not extend longitudinally along the photo-multiplier tube55. Rather, the support rings 102 extend around the circumference of thephoto-multiplier tube 55, and are spaced out in intervals along itslength.

FIG. 7 shows the scintillation element 50, photo-multiplier tube 55 andelectrical elements 57 supported by the support mechanism 100. In FIG.7, the support rings 102 are shown at different radial elevations withrespect to the supported components 50, 55, 57. The support rings 102 atdifferent radial elevations do not have to be concentric and can bespaced apart along the length of the protected elements 50, 55, 57. FIG.8 shows a close-up view of the support mechanism 100. The support rings102 are separated by the metal tape or retainer 106. The support rings102 do not extend axially along the length of the photo-multiplier tube55. Rather, the support rings 102 are spaced apart axially, and extendaround the circumference of the photo-multiplier tube 55.

If the first housing 58, the tolerance rings 102 and thephoto-multiplier tube housing 120 are of the same material, or materialwith equivalent thermal expansion coefficient, there will be very littledifferential expansion due to thermal changes. In applications where thevibration and shock are the most serious environmental challenges andthermal changes are not significant, the choice of materials may not bevery significant. In applications such as down-hole drilling for oil andgas, careful attention must be paid to the selection of compatiblematerials to avoid significant thermal expansion.

It should be noted that in a preferred embodiment, the housing aroundthe photo-multiplier tube 55 is rigidly connected to a crystal outerhousing so that the crystal outer housing and the photo-multiplier tube55 do not move relative to each other. Therefore, if the support rings102 do not allow excessive motion in the radial direction of thephoto-multiplier tube housing 120 relative to the first housing 58, thenthe photo-multiplier tube 55 would be held sufficiently well relative tothe window 52 of the housing and crystal package combination.

If the support rings 102 are made from soft materials, such aselastomers, then they would tend to have a low resonant frequency and arelatively high dynamic transmissibility. This is known to haveundesirable consequences. If the rings are made from a rigid materialsuch as solid steel, then the tolerances of all the mating parts wouldhave to be made extremely precise to prevent the elements from beingloose, and they would have to be installed in a tight tolerancecondition. Yet, if the support rings 102 are tight and rigid, then anyerrors in tolerances would render the support rings 102 difficult orimpossible to install without damaging the delicate instruments. Someinstruments for harsh environments are known to be designed in just thismanner, and are known to be costly to manufacture. The solution is touse support rings 102 that are made from a strong material, such asstainless steel, but configured such that the support rings 102 havesome elastic properties.

In order to conserve valuable space within the detector or other similartool, the support rings 102 need to be very thin. In use, unique designparameters for the support rings 102 are selected to meet particularrequirements of the application for which the support rings 102 areused. Some of the particular requirements are as follows.

The overall thickness of the support rings 102 is selected to fill gapsand tolerances between two components, and selection of appropriatetolerance rings is made using vendor catalog data. Friction forcesexerted by the support rings 102 must be sufficient to prevent relativelongitudinal motion between two components due to vibration forces,while the size of the support rings 102 must remain small enough toallow ease of assembly. Examples of nominal friction forces are 40pounds-force for a 1 inch×4 inch detector, and 125 pounds-force for a 2inch×10 inch detector. Support ring 102 data, provided by vendors,includes: Torque; Capacity; Diametral Clearance; material thickness; andcorrugation pitch. These and other parameters are used to determine theappropriate support ring characteristics.

Another consideration when selecting a support ring 102 is protection ina high vibration environment. This is achieved by a natural vibrationfrequency of the combination of the component and support ring. Thenatural vibration frequency should not adversely couple with thevibration loads of the environment. Vibration environments that must beprotected against are typically in the 100-200 Hz range. Thus, supportrings 102 would typically be designed to provide a natural vibrationfrequency greater than 300 Hz. Stiffness of the support ring is the keyparameter used to control the natural vibration frequency. Support ringvendor catalogs typically provide data used to determine support ringstiffness.

Still another consideration is to provide adequate structural support tocomponents in order to prevent structural failure due to damagingacceleration loads. Multiple support rings 102 may be used along thelength to provide support as needed to reduce mechanical stress.Traditional stress analysis techniques are used to determine where andhow many support rings are needed.

Use of the support rings 102 in the present invention results in adesirable support mechanism 100. The support rings 102 can be selectedand installed to provide resistance to movement in the longitudinaldirection within acceptable limits while limiting the movement in theaxial direction to a few thousands of an inch. Thus, the support system100 comprising the support rings 102 protects optical coupling elementsfrom excessive stress.

The present inventions offer several advantages, as follows. Theinventions provide a lower cost method of supporting instrumentationpackages and sensors using off-the-shelf commercial parts. Theinventions provide a more convenient method of delivering stiff supportto an undersized component fitted into a standard sized housing (i.e.,filling of the gap and tolerance). Also, when two parts of a detectorassembly (e.g., electronics and crystal elements) that have differentdiameters are assembled into a common housing, use of tolerance ringsallows the parts to be assembled without using sleeves to increase thesmaller diameter. Another desirable result is that a lesser amount ofradiation is blocked from entering into the scintillation element.

Unlike flexible sleeves and flexible dynamic housings that must extendalong the length of the scintillation element, the support mechanism 100having support rings 102 supports only at two or more locations of thescintillation element. This is possible because of the relative highstiffness of the support ring 102 due to the curved shape of the bumps104. If the support ring 102 has a rim 108, i.e., the bump 104 does notextend the full height 110 of the support ring 102, the ring will beeven stiffer. This improves optical performance of the scintillationelement. Since tolerance rings support only at locations of thescintillation element, this leaves a significant portion of thereflective tape along the length of the scintillation element notcompressed, and uncompressed reflective tape has superior opticalperformance.

In addition, the support mechanism having support rings 102 works wellwhere the annular gap between the photo-multiplier tube and its rigidhousing is not uniform. Because the support rings do not extend alongthe axial length of the photo-multiplier tube, variances in the gapdimension in one location will not affect the dynamics of the system inanother location. Each support ring 102 acts independently of othersupport rings 102.

It should be recognized that there are alternative methods of applyingthe compound coupler and support rings to a scintillation element. Forexample, one method is to use wraps of teflon and steel between thescintillation reflector 67 and the support rings 102. The scintillationelement 50 is wrapped with teflon tape to about 0.03 inches,uncompressed, or with approximately 0.015 inches thick sheet of skivedteflon to serve as a reflector. A thin layer of stainless steel, ideally0.002 inches to 0.005 inches thick, is then wrapped around the teflonreflector, with the joint of the stainless steel wrap positioned on theopposite side of the scintillation element 50 from the joint of theskived teflon sheet. The inside surface of the steel wrap can be coatedwhite, or with a reflective material to provide additional reflection ofany light that may pass through the teflon reflector. Support rings 102are then placed around this assembly with tape or bonded material tohold the rings in place, similar to the way elements 106 in FIG. 8 areused in the embodiment described earlier.

Another method is to wrap the reflector 67, which is around thescintillation element 50, with two layers of stainless steel, the insidesurface of the inside layer of stainless steel being coated with areflecting material. The two layers of stainless steel would beseparated by an elastomeric material that is molded or bonded, in theform of ridges or strips, to the surface of one of the layers (similarto the ridges of sheath 81 in FIG. 3). This approach is low cost andreduces the compression forces due to the expansion of the scintillationelement 50 during temperature changes so that the support rings 102 maybe a stiffer configuration to make installation simpler.

The compound optical coupler of the invention will now described withreference to FIG. 9, which shows in greater detail the first opticalcoupler 51, the window 52 and the optical coupler 53 of FIG. 2. Theinvention provides a compound optical coupler that transmits lightpulses from a scintillation element 50 into the light detector device(e.g., photomultiplier tube 55). To accomplish this, the inventionincludes a self-wetting clear optical coupling gel 202, which can beWacker, for example, and a special elastomeric load ring 204, which canbe Sylgard, for example. Alternatively, the load ring 204 can compriseanother rubber-type material.

The elastomeric load ring 204 is molded or otherwise attached to theface of the photomultiplier tube 55 and the window unit 52 to form anannular ring with an outer diameter that is preferably the same as thatof photomultiplier tube 55. The inner diameter of the load ring 204 issized based on the forces that it must withstand. A self-wetting opticalmaterial is then poured into the inner annulus of the load ring 204,forming a slightly convex surface. The convex surface allows for goodcontact with the self-wetting coupler material prior to engaging theelastomeric load ring 204, thus providing a good optical interface.

The drawbacks associated with previous attempts to use a self-wettingclear material in an optical coupler are circumvented by the presentinvention which uses an elastomeric load ring 204. The elastomeric loadring 204 made from an elastomeric material can be bonded, or otherwiseattached to the light detector device (e.g., photomultiplier tube 55) orto a window of a scintillation element 50 as an annular ring outside theprimary light paths. The elastomeric load ring 204 serves as: (1) theprimary load path to maintain the interface forces between thescintillation element 50 and the light detector device; and (2) as aretainer ring to prevent migration of the soft self-wetting clearmaterial 202 from the interface. The result is an interface between thescintillation element 50 and light detector device that is self-healing,is pliable enough to maintain a clear bubble-free interface underextreme loads and vibration, and is more tolerant of fabrication and/orassembly tolerances.

Another preferred embodiment for a support mechanism will now bediscussed with reference to FIGS. 10-15. With reference to FIG. 10, agamma detector 250 having a support mechanism 300, which will bedescribed in greater detail below. The gamma detector 250 has ascintillation element 50 (or “crystal”) and a photo-multiplier tube 55(or “PMT”) separated by an optical coupler 252, which may be a compoundoptical coupler as described above. A photo-multipliertube/scintillation element separation plane is represented by numeral266. The gamma detector 250 has a wire insulator 254, wire clearancesupport 256, a hermetic feed through part 260 and an end fitting 258 toaccommodate wires coming from the photo-multiplier tube 55.

The gamma detector 250 has a photo-multiplier tube housing 264 and ascintillation element housing 268. The photo-multiplier tube housing 264is a solid housing, whereas the scintillation element housing 268 is asplit housing. The split housing 268 helps restrain the scintillationelement crystal at the photomultiplier tube interface, and functions tolock the PMT and crystal together. A reflective layer 274, which in apreferred embodiment may be a teflon reflective layer, is locatedinterior of the housings 264, 268. As shown in FIG. 10, the gammadetector 250 has a reflector 272, and a longitudinal clearance 270between the reflector 272 and housing 268. The gamma detector haslongitudinal support springs 262 and an outer housing assembly 276. Theouter housing assembly may comprise multiple layers of housings, asdescribed and illustrated above with respect to gamma detector 250.

The support mechanism 300 is illustrated in greater detail in FIGS. 11and 12. The support mechanism 300 comprises friction rings 302 and shockrings 330. In a preferred embodiment the shock rings 330 are elastomericO-rings comprising viton rubber and having a durometer of 75. Thefriction rings 302 and O-rings 330 are disposed between the outerhousing assembly 276 and scintillation element housing 268 orphoto-multiplier tube housing 264. With reference to FIG. 12, anotherpreferred embodiment of the support mechanism 300 has friction rings 302and O-rings 330 disposed between the outer housing assembly 276 and anouter support housing 278. In the embodiment of FIG. 12, a lubricant 280is disposed between the outer support housing 278 and housing 264, 268.

The friction rings 302 are described in more detail with reference toFIGS. 13-15. The friction ring is made from a corrugated sheet 320. In apreferred embodiment, the friction ring comprises 17-7 PH Condition Cstainless steel, heat treated to CH 900 after being formed into itsfinal shape. The corrugated sheet of metal 320 has peaks 304 and flatportions 306. The corrugated sheet 320 has a length 308, a width 310, aheight 312 and a thickness 314. In a preferred embodiment, the width 310is between approximately 0.25 and 1.0 inches, and the height 312 isbetween approximately 0.010 and 0.10 inches. The length is chosen toaccommodate the circumference of the scintillation element 50 and/orphoto-multiplier tube 55. As shown in FIG. 15, the ends of thecorrugated sheet 320 are brought together to form the friction ring 302,having a gap 316 between ends of the sheet 320.

The number of the friction rings 302 is chosen depending on theconfiguration of the gamma detector 250. In an exemplary embodiment,between four and seven friction rings are used. The friction rings 302do not extend longitudinally along the gamma detector 250. Rather, thefriction rings 302 extend around the circumference of thephoto-multiplier tube 55 and/or scintillation element 50, and are spacedout in intervals along its length. The friction rings 302 may bedisposed at different radial elevations with respect to the supportedcomponents 50 and 55, as discussed and illustrated above with respect tosupport rings 102. The friction rings 302 at different radial elevationsdo not have to be concentric and can be spaced apart along the length ofthe protected elements 50, 55.

In use, the gamma detector's inner assembly—the scintillationelement/photo-multiplier tube and reflective layer 274—is supported bythe friction rings 302 most of the time during operation. Typically, thefriction rings 302 provide static support to the inner assembly foracceleration forces of up to 30 Gs, but not more than 50 Gs, where G isthe acceleration due to gravity. The numerical value for theacceleration of gravity G is most accurately known as 9.8 m/s², withslight variations dependent primarily upon on altitude.

During most of the operation, the O-rings 330 do not provide support tothe inner assembly. When the shock exerted on the gamma detector 250exceeds the threshold of the static support of friction rings 302, theinner assembly will begin to move, or slide, relative to the surfaces ofthe friction rings 302. Such sliding friction is a very effectivedamping mechanism. During high shocks, in the range of 200 G to 1000 G,the friction rings 302 cannot prevent the inner assembly from moving tothe point of impacting the housings 264,268. During such high shocks,the O-rings 330 function as shock absorbers that limit movement of theinner assembly such that the inner assembly does not impact the housings264, 268. In case the inner assembly does impact the housings 264, 268,the O-rings 330 function to ensure that the effect of the impact is notdamaging.

During high shocks, each friction ring 302 does not allow movement ofthe inner assembly at the same instant, and friction forces between thefriction rings and the inner assembly are reduced once movement, orsliding, begins. At this time, the O-rings 330 function to distributethe friction forces and to miximize movement of one portion of the innerassembly relative to other portions of the inner assembly. To accomplishthis function, in a preferred embodiment the outside diameter (O.D.) ofthe installed O-rings 330 will typically be slightly smaller than theinside diameter (I.D.) of the housings 264, 268. A small amount ofmechanical interference between the O-rings 330 and the housings 264,268 will not impair the quality of the support mechanism 300. However,such mechanical interference may complicate installation of thecomponents of the support mechanism 300, and may result in problemscaused by differential thermal expansion of the components.

If the tolerances of the inner assembly and/or the rate of temperaturechange in parts of the inner assembly results in one portion of theinner assembly being more tightly held by the O-rings 330 than anotherportion, the photo-multiplier tube 55 may be pulled away from thescintillation element 50. Therefore, in a preferred embodiment, the O.D.of the installed O-rings 330 is slightly smaller than the I.D. of thehousing 276. An exemplary difference between the O.D. of the O-rings 330and the I.D. of the housing 276 is approximately 0.002 inches.

Dimensions should be controlled to prevent excessive compression of theO-rings 330 when the diameter of the inner assembly, including O-rings330, is on the high side of its diametrical tolerance and/or the I.D. ofthe housing 276 is on the low side of its tolerance. In an exemplaryembodiment, a suitable tolerance for an assembly for a scintillationcrystal one inch in diameter is ±0.004 inches, and a suitable tolerancefor the I.D. of the housing 276 is ±0.002 inches.

Friction rings 302 could be made from a thicker material, so that thefriction forces between the friction rings 302 and the inner assemblywould not be overcome even during high shocks up to 1000 Gs. O-rings 330would not be needed in such a configuration. However, such aconfiguration for the support mechanism 250 would not be compliant whentemperature cycles as high as 175° C., or even higher in someapplications. The consequences would likely be excessive pressure on theentire assembly due to thermal expansion differential. Such differentialexpansion could damage the inner assembly, and, for example, cause theface of the photo-multiplier tube 55 to be pulled away fromscintillation element 50.

A desired characteristic of the support mechanism 300 is that the use offriction rings 302 produces a support mechanism with a high resonantfrequency. A support mechanism with high resonant frequency will notresonate with lower frequency vibrations that pass through the outerhousing assembly 276. The support mechanism 300 provides a very rigidconfiguration under high vibration conditions. High vibrationconditions, up to approximately 30 G, are typically experienced bymining equipment, whether for coal, potash, trona, oil or gas cuttingand/or drilling operations. During the high vibration conditions, thefriction rings 302 are essentially not movable, or “locked up” in thesupport mechanism 300, producing a rigid assembly having a high resonantfrequency.

Because each peak 304 of the friction rings 302 is pressed againsteither the outer surface of the inner assembly or against the innersurface of the housings 264, 268, movement between the rings and thesurfaces will be constrained by friction forces (unless high shocksovercome the friction forces). For vibration forces up to the designatedrelease point at which the inner assembly begins to move with respect tothe friction rings 302, which typically occurs between 30 G and 50 G,the peaks 304 will not slide relative to the surface of the innerassembly. Under such conditions, the portions of the flat portions 306between the peaks 304 will be in either compression or tension, ratherthan bending.

Even though the friction rings 302 are formed from a thinmaterial—typically 0.002 to 0.006 inches thick—when constrained in themanner described and illustrated, compression forces pass throughcorrugated side walls 307 of the friction ring 302 material between thepeaks 304. Such a configuration provides high stiffness.

When the shock overcomes the frictional forces between the frictionrings 302 and the inner assembly, however, the friction ring peaks 304begin to slide relative to the surfaces of the inner assembly or thehousings 264, 268. At such time the friction resistance will be reducedin magnitude, since sliding friction is less than static friction. Asthe inner assembly moves to one side of the gamma detector 250, thepeaks 304 will be forced to spread, and the friction ring material willexperience significant bending forces. The resonant frequency is reducedsignificantly during such sliding as the overall stiffness of theassembly is greatly reduced.

During such high shock events, when the resonant frequency dropssignificantly and the movement or displacement of the inner assemblybecomes large, the sliding friction provides excellent damping. Once thesliding begins under high shock, the O-rings 330 absorb the energyproduced by the relative motion of the inner assembly. The damping fromthe sliding friction prevents the build-up of low resonant frequencyeven though a significant part of the motion restraint is due to theO-rings 330, which have a relatively low stiffness that would allow lowresonance frequency to build up if not adequately damped. In addition,as soon as the dynamic forces, which sustain relative motion between theinner assembly and the housings 264, 268, drop below the threshold valueof the sliding friction, the inner assembly will once again be capturedand restrained by the friction rings 302.

Design considerations for an exemplary embodiment of a detector havingthe support mechanism 300 will now be discussed. Successful design of ascintillation detector using the support mechanism 300 of the inventionincludes the O-Rings 330, friction rings 302, and housings 264, 268 withgrooves to maintain proper alignment and spacing of the friction rings302 and O-rings 330 during installation. In a preferred embodiment,housings 264, 268 comprise a PEEK liner. The PEEK liner is a hardsurface for the friction rings 302 to press against and spread out theload. For large gamma detectors used for mining minerals such as coal,potash, or trona, the design parameters will typically be as describedbelow. These parameters may be adjusted to satisfy application specificdesign parameters, or engineering and/or manufacturing preferences. Forexample, one adjustment that might be desired would be to increase thenumber of friction rings 302 for applications where the vibration levelsmight be above 25 Grms, in order to maintain friction support. GRMS isthe root-mean-square acceleration (or rms acceleration), which is thesquare root of the mean square acceleration. Mean-square acceleration isthe average of the square of the acceleration over time. Adding morefriction rings 302 adds more steel around the scintillation element 50.Such would block radiation from reaching the scintillation element 50,so it would not normally be done unless needed for dynamic support underhigher vibration levels. Changes should not normally be required forshock considerations since the typical practice would be to add anO-Ring 330 for each friction ring 302 added.

Operation effectiveness of a particular design for a support mechanism300 can be easily verified by measuring the force on the end of thescintillation element 50 required to break static friction between thefriction rings 302 and the inner assembly—when the inner assembly beginsto slide relative to the friction rings 302. This force should be about30% to 50% greater the force that is expected to result from worst casescenario vibration levels. Incidental shocks are generally notconsidered because the O-rings 330 will serve as shock absorbers afterthe static friction between the friction rings 302 and the innerassembly has been exceeded. This force is simply calculated as theproduct of the weight of the scintillation element 50 and the G levelsbeing designed for. For example, if the worst case vibration level isexpected to be 15 Gs, and the scintillation element 50 weights 0.5pounds, the force required to push the scintillation element 50 shouldbe approximately between 10 pounds and 12 pounds. This can be easilychecked during prototyping by use of a simulator of the scintillationelement 50, and can be checked during production as frequently as deemeduseful for the assembly process being used. If a prototype is designedusing the following exemplary guidelines and is found by testing to nothave adequate friction resistance, additional friction rings 302 can beadded. Fewer friction rings 302 can be used, but such should be donewith caution if there is a chance of the detector receiving high shocksduring handling or operational use.

Although the design guidelines are discussed with respect to ascintillation element, they are equally applicable to a completeradiation detector assembly which also may include accelerometers, rategyros, power supplies, microprocessors and other elements. For asituation where a small scintillation element 50 is used together with alarge electronics module, the number of friction rings 302 and O-rings330 can be reduced for the end of the detector which supports theelectronics module and/or the number of friction rings 302 used on theheavier end of the detector, having the scintillation element 50, may beincreased. For special cases, good engineering judgment must be used.Fortunately, if testing of a new design indicates a problem, the numberof friction rings 302 can easily be changed without a major re-start ofthe development process.

Use of friction rings 302 for support allows the design process to begreatly simplified over earlier support mechanisms, such as flexibledynamic housings and flexible sleeves. To illustrate the simplified andstraightforward process, typical design parameters for the two majorcategories of scintillation element 50 sizes are discussed below. Onetypical size category is for scintillation element 50 crystals that arebetween 0.75 and 1.25 inches in diameter, and the other category is forscintillation element 50 crystals between 1.75 and 2.5 inches indiameter. The following parameters are suitable for complete gammadetectors that include scintillation elements 50, photomultiplier tubes55, electronics and the like.

Important parameter selections for scintillation elements between 1.75and 2.5 inches in diameter include the dimensions of the friction rings302, the number of friction rings 302, dimensions of the O-rings 330,the number of O-rings 330, radial spacing between elements, and thepitch 305, which is the distance between adjacent peaks of the sheet 320from which friction rings 302 are made. The PEEK liner 264, 268 betweenthe scintillation element 50 and the inside diameter of the outerhousing 276 would typically have a wall thickness of approximately 0.070inches, and the diameter would be selected to leave a gap ofapproximately 0.030 inches between the PEEK liner and the shield.

Grooves 380 should be cut into, or otherwise formed in the PEEK liner toretain the friction rings 302 (FIG. 16). Making such grooves 0.035inches deep, and making the friction ring waves 306 to have a height 312of 0.080 inches would, in use, compress the friction rings 302 by 0.015inches. Similarly, use of standard O-rings 330 that are 0.070 inches indiameter, and making O-ring grooves 0.045 inches deep would leave theO-rings 330 with no compression, so that the O-rings 330 would not berestraining the scintillation element 50. Rather, the O-rings 330 wouldfunction to cushion the scintillation element 50 when shock forcesexceed the friction forces. It is acceptable to choose dimensions sothat there is a nominal, small gap between the O-rings 330 and theinside diameter of the shield. Ideally, there will be less than 0.010inches of compression on the O-rings 330 at high temperatures, includingtolerances, and the gap at cold temperatures, including tolerances,would be less than 0.010 inches. In a preferred embodiment, O-rings 330are viton O-rings having a hardness durometer of 75. The O-ring grooves380 in the PEEK liner 264, 268 restrain movement of the O-rings in alinear direction.

In a preferred embodiment, a typical arrangement of friction rings 302and O-rings 330 would be to place friction rings 302, having a width of0.5 inches, at approximately 1.5 inches from each other along the lengthof a scintillation element 50. One O-ring 330 would be place betweeneach pair of friction rings 302. With this arrangement, the number ofO-rings 330 will be one less than the number of friction rings 302. Thenumber of friction rings 302 and O-Rings 330 is dependent on the lengthof scintillation detector.

Important parameters, typical for smaller scintillation elements 50having diameters between 0.75 and 1.25 inches, are described below.Since the mass of scintillation elements 50 in this size range issmaller than for larger scintillation elements described above, thecharacteristics of the support mechanism 300 can be changed to allowmore room for needed detector elements. Many gamma detectors used forwireline applications, such as logging coal or potash formations, andmost Measurement While Drilling or Logging While Drilling applicationsfor oil and gas drilling operations, utilize smaller scintillationelements 50, since the gamma detectors must fit within the drilling orlogging tools. Logging of mineral formations could, in rare instances,incorporate larger scintillation element crystals, and in suchcircumstances the design parameters discussed above would be applicable.Parameter values may be adjusted as needed according to good engineeringjudgment. However, once the information in this specification isunderstood, complex analysis should not be required to select theseparameter values.

With reference to FIG. 16, the PEEK liner, having 0.040 inch thickwalls, with a longitudinal slit approximately 0.090 inches wide alongthe entire length of the PEEK liner is provided. The outer diameter ofthe PEEK liner is 0.034 inches smaller than the inner diameter of theouter housing assembly 276. Circumferential grooves 380 in the PEEKliner, which is formed into a tube, are included to retain in place thefriction rings 302 and O-rings 330 during and after assembly. Grooves0.525 inches wide by 0.020 inches deep are incorporated into the PEEKliner to accommodate friction rings that are 0.5 inches wide. Similarly,grooves 0.040 inches wide by 0.015 inches deep in the PEEK lineraccommodate O-rings having a cross-section diameter of 0.032 inches.

Design parameters for friction rings 302 in a preferred embodiment areas follows. In a preferred embodiment, friction rings 302 have a widthof 0.5 inches, a height of 0.035 inches, and pitch of 0.25 inches. In apreferred embodiment, circular O-rings 330 are made from Viton rubber,having a cross-sectional diameter of 0.032 inches. The O-rings 330 havean outer diameter that is 0.024 inches greater than the outer diameterof the PEEK liner tube. Such a configuration provides a gap between theouter diameter of the O-Ring and the sleeve. Thus, as discussed above,the O-rings 330 do not function to restrain the inner assembly undernormal low shock operations.

An installation liner 428 (shown in FIG. 17), which in a preferredembodiment is made from 0.002 inch thick stainless steel wrap, isinstalled around the outside of the friction rings 302 and O-rings 330to facilitate installation of the support mechanism 300 into the sleeve.The installation liner 428 covers the assembly so that when it isinstalled into the outer housing assembly 276, the friction rings 302and O-rings 330 do not become caught on any rough surfaces anddisplaced.

Manufacturing considerations for a support mechanism 300 according to apreferred embodiment are now discussed. The PEEK liner is fabricated bymachining a section of PEEK tube, or solid PEEK material, to thedimensions described above in the design considerations section. Thefabrication of the PEEK liner includes cutting of a 0.090 inch widelongitudinal slit 382 along the PEEK liner, which is formed into a tube.PEEK is known to be suitable for use as a liner around a sodium iodidecrystal since it has a thermal coefficient of expansion of approximatelyequal to that of the crystal. The PEEK material, after being baked at200 degrees C., will not off-gas or lose its mechanical properties as domany plastic materials.

Manufacture of friction rings typically starts with cutting 0.5 inchwide strips from a 17.7 Ph stainless steel that is 0.002-0.006 inchesthick. Such stainless steel is a condition C material. Length of suchstrips is optional. It is desirable, however, that the sheets 320 belong enough to fabricate several friction rings 302 from one strip. Eachof the 0.5-inch-wide strips is run between wave shaping wheels on aBeading Machine to create the wave shapes 306 of the friction ring 302.An example of such a Beading Machine is Model 0581 from the RoperWhitney Company. After shaping the waves 306 into the 0.5 inch widestrips, the strips are cut into sheets 320 having a length 308 equal tothe circumferential length of the individual friction ring 302. In apreferred embodiment, the length 308 is equal to L=0.95·π·D. Forexample, the length 308 for a sheet 320 for use with a 1 inch diameterscintillation element crystal would be 2.98 inches. After the frictionrings 302 are cut to a proper length 308, the friction rings 302 shouldundergo heat-treatment to raise the material strength to conditionCH900.

Assembly considerations for a support mechanism 300 according to apreferred embodiment are now discussed. Initially, all mechanical partsare cleaned and gathered to prepare for assembly. The window unit isbonded to the two part optical coupler, as discussed above, andthereafter the window unit is welded to the housing. At this stage, allmoisture is baked out from all of the parts. Next, the scintillationelement crystal is compensated, and the scintillation element crystalinterface is polished. Compensation is a preparation procedure for theouter surface of the crystal so that it will reflect light for optimumperformance.

The scintillation element crystal is next wrapped with, in a preferredembodiment, three layers of compressed Teflon tape, and the Teflon tapeis covered with reflective layer 274. Next the PEEK liner is installedover the scintillation element crystal package. The support mechanism300 is further assembled by installing O-rings 330 in grooves of thePEEK liner, and friction rings 302 are installed into grooves of thePEEK liner. In a preferred embodiment, a tape such as kapton tape isused to secure the friction rings into the grooves of the PEEK liner.

Next, the PEEK liner 264, 268 is wrapped with a 0.002 assemblyinstallation tool, and the assembly is installed into the outer housing276. A reflector 272 is then placed onto a rear surface of thescintillation element crystal 50, and compression plates and shims 263are added to the rear surface of the scintillation element crystal.Thereafter, longitudinal support springs 262, which in a preferredembodiment comprise wave springs, are installed the rear ofscintillation crystal package with enough linear force to override thefriction force of the friction rings by approximately 25%. The end capis then installed and welded into place.

Assembly considerations for another support mechanism 300 according to apreferred embodiment are now discussed. All mechanical parts are cleanedand prepared for assembly, which is started by welding an end cap ontothe housing. The photomultiplier tube 55 is packaged into the housing264, and the two-part optical coupler is bonded onto the photomultipliertube 55, as discussed above. There after, a hermetic feed-thru 260 isinstalled onto the photomultiplier tube 55. At this stage, all moistureis baked out from all of the parts.

The scintillation element crystal is then prepared for assembly asdiscussed above. Namely, the scintillation element crystal iscompensated, and the scintillation element crystal interface ispolished. The scintillation element crystal is next wrapped with, in apreferred embodiment, three layers of compressed Teflon tape, and theTeflon tape is covered with reflective layer 274. Next the PEEK liner isinstalled over the scintillation element crystal package. The supportmechanism 300 is further assembled by installing O-rings 330 in groovesof the PEEK liner, and friction rings 302 are installed into grooves ofthe PEEK liner. In a preferred embodiment, a tape such as kapton tape isused to secure the friction rings into the grooves of the PEEK liner.

The assembly process continues by inserting the scintillation elementcrystal package into photomultiplier tube package, with the polished endof crystal resting against the optical coupler. The photomultiplier tubeand scintillation element crystal are then placed into an assemblyfixture. A reflector is placed onto the rear of the scintillationelement crystal, and compression plates and shims are added on the rearof scintillation crystal package. Thereafter, wave springs 262 areinstalled on rear of the scintillation element crystal package, withenough linear force to override the friction force of the friction rings25%, approximately.

The assembly is completed by wrapping the scintillation element crystalpackage and the photomultiplier tube package with a 0.002 installationtool, as discussed above. The housing is then installed overscintillation element crystal package and photomultiplier tube package,so that the housing is completely seated onto the hermetic feed thru260. The feed thru 260 is welded to the housing, and the unit is thermalcycled prior to performing any tests. Then, wires are installed onto thefeed thru 260. Finally, appropriate detector ends 265 are installed ontothe detector, and performance and environmental testing can begin.

An embodiment of the PEEK liner 264, 268 is shown in FIG. 16. The PEEKliner 264, 268 has grooves 380 into which friction rings 302 and O-rings330 are installed, as discussed above. The PEEK liner 264, 268 also hasa longitudinal slit 382, as shown. The dimensions shown in FIG. 16 arein inches, and are only an example of a configuration according to apreferred embodiment of the PEEK liner 264, 268.

Refer now to FIG. 17, which shows a cross-sectional view of an assembleddetector having a support mechanism 300 in accordance with an embodimentof the present invention. FIG. 17 shows the outer housing 276 having athickness 410, and having a clearance 412 between it and the PEEK liner264, 268. The outer housing 276 has a clearance 414 between it and theO-ring 330 (not shown in FIG. 17). The outer housing 276 has an insidediameter 416 and an outside diameter 418. FIG. 17 also shows the PEEKliner thickness at the O-ring 330 represented by numeral 420, and atfriction ring 302, represented by numeral 422. The scintillation elementcrystal has a diameter 424. Clearance between the PEEK liner and theinside diameter of the outer housing 276 is represented by numeral 426.

In a preferred embodiment, the housing thickness 410 is 0.045 inches,and the inside diameter 416 is 2.223 inches and the outside diameter 418is 2.313 inches to accommodate a scintillation element crystal having adiameter 424 of 2 inches. The PEEK liner thickness 420 (at O-ring) is0.025 inches, and the PEEK liner thickness (at friction ring) 422 is0.035 inches. The available clearance 412 between the friction rings 302and the outer housing 276 is 0.065 inches. The available clearance 414between the O-rings 330 and the outer housing 276 is 0.075 inches. Theclearance 426 between the PEEK liner 264, 268 and the inside diameter ofthe outer housing 276 is 0.030 inches. In the embodiment of FIG. 17, thefriction ring 302 has a height of 0.080 inches at 0.50 pitch, and theO-ring 330 has a diametrical cross-section of 0.070 inches, and aclearance of 0.005 inches to the internal diameter of the outer housing276.

While the invention has been described in detail in connection withpreferred embodiments known at the time, it should be readily understoodthat the invention is not limited to such disclosed embodiments. Rather,the invention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention.

1. A scintillation element package, comprising: a scintillation element;an outer housing encompassing said scintillation element; and a supportmechanism including at least one friction ring, said support mechanismbeing between said scintillation element and said outer housing.
 2. Thepackage of claim 1, wherein said at least one friction ring has at leasttwo peaks and a flat portion between said at least two peaks.
 3. Thepackage of claim 1, wherein said support mechanism further comprises atleast one O-ring.
 4. The package of claim 1, further comprising a linerbetween said at least one friction ring and said scintillation element.5. The package of claim 4, wherein said liner is a PEEK liner comprisinggrooves for accommodating each of said at least one friction ring.
 6. Aphoto-multiplier tube package, comprising: a photo-multiplier tube; aouter housing encompassing said photo-multiplier tube; and a supportmechanism including at least one friction ring, said support mechanismbeing between said photo-multiplier tube and said outer housing.
 7. Thepackage of claim 6, wherein said at least one friction ring has at leasttwo peaks and a flat portion between said at least two peaks.
 8. Thepackage of claim 6, wherein said support mechanism further comprises atleast one O-ring.
 9. The package of claim 6, further comprising a linerbetween said at least one friction ring and said photo-multiplier tube.10. The package of claim 9, wherein said liner is a PEEK linercomprising grooves for accommodating each of said at least one frictionring.
 11. A support mechanism comprising: a photo-multiplier tube; ascintillation element; a liner disposed around said photo-multipliertube and said scintillation element; and at least one friction ringaround said liner.
 12. The support mechanism of claim 11, wherein saidat least one friction ring has at least two peaks and a flat portionbetween said at least two peaks.
 13. The support mechanism of claim 11,wherein said liner is a PEEK liner comprising a groove for accommodatingeach of said at least one friction ring.
 14. The support mechanism ofclaim 11, further comprising at least one O-ring.
 15. A gamma detectorassembly, comprising: a photo-multiplier tube; a scintillation element;a liner disposed around said photo-multiplier tube and saidscintillation element; and at least one friction ring around said liner.16. The gamma detector assembly of claim 15, wherein said at least onefriction ring has at least two peaks and a flat portion between said atleast two peaks.
 17. The gamma detector assembly of claim 15, whereinsaid liner is a PEEK liner comprising a groove for accommodating each ofsaid at least one friction ring.
 18. The gamma detector assembly ofclaim 15, further comprising at least one O-ring.
 19. The gamma detectorassembly of claim 15, further comprising an optical coupler between saidphoto-multiplier tube and said scintillation element.
 20. The gammadetector of claim 19, wherein said optical coupler is a compound opticalcoupler.